+1 I am interested in something similar. I have an excellent B737 panel in FS2004 with active switches (they toggle) for both Fasten your seatbelts and No smoking signs. Unfortunately when you toggle them you hear NOTHING, not even a boring click.

In my FS9 sounds directory there is a "signs.wav" file that plays the familiar ding-dong sound as in real a/c. This sound is used in some other gauge of another panel.

Now, HOW do I make these two switches emit that sound? it is something that adds to the feeling of realism short of having actual voice announcements but it is often disregarded by panel designers.